(a) Field of the Invention
The present invention relates to epoxy resin compositions for semiconductor sealing which can be transfer molded to produce full-molded type packages with different resin thickness for the marking side and the back, such as full-molded type power TRS (FM-type P-TRS), without leaving voids, and also to resin molded type semiconductors sealed with the epoxy resin compositions.
(b) Description of the Related Art
Resin molded type semiconductor devices are produced by sealing semiconductor elements, such as ICs, LSIs, TRSs or diodes, with thermosetting resins to protect them from the external atmosphere and mechanical shock. From the viewpoints of mass-productivity, cost and reliability, low pressure transfer molding with epoxy resin compositions, which suits mass production, is widely used to seal semiconductor elements.
The diversity of the package forms of recent resin molded type semiconductor devices increases packages having forms difficult to mold, including TSOPs (thin single outline packages), which are ultra thin packages 1 mm thick or less, and packages containing radiator plates, being about 10 mm thick and having different resin thickness for the marking side and the back, such as full-molded type transistors (FM-type TRSs), full-molded type power transistors (FM-type P-TRSs) and full-molded type ICs (FM-type ICs).
When a conventional epoxy resin composition for semiconductor sealing (hereinafter, may be called sealing resin) are transfer molded to produce packages with different sealing resin thickness for each side of an insert, such as FM-type TRSs, FM-type ICs or FM-type P-TRSs, the behavior of the sealing resin flowing into the cavity is different for the upper side (the marking side) and the lower side (the back), and makes weld marks (a kind of voids which are left at the joining points of the upper resin and the lower resin flowing separately on and under the insert during filling the cavity with the resin) on moldings. The weld marks decrease the electric properties (such as insulation voltage) and reliability in moisture resistance of resin molded type semiconductor devices. For example, when the moisture resistance is tested by a PCT at 120.degree. C. in a steam of 2 atm, water enters from the weld marks and causes a leakage current and breakage of electrodes due to corrosion and, at a high voltage, decreases the insulation properties.